First you need AutoCast from Google Play
Unzip attached xml file and save it under Tasker/task
Import the file in tasker by holding down the TASK tab and select Import.
Open GOOGLE_HOME_SPEAKER
Open Auto Cast on line 3, press the pen, select Cast Device and select your Google Home.
Go back several step to main menu press the check mark Icon to save and reload tasker.

Now we are ready to create our first message from HS3.
Create an event and select Control a device, select your tasker device and custom code.
Use this syntax,GOOGLE_HOME_SPEAKER=:=Hello, this is a test on google home.
You can also send a volume factor. Default is 100GOOGLE_HOME_SPEAKER=50=:=Hello, this is a test on google home.
You can as Always also use replacement variables.GOOGLE_HOME_SPEAKER=:=The spa temparature is now $$DVR:876: degrees